The present application is based on and claims priority from Japanese Patent Application 2000-054701, filed Feb. 29, 2000 and 2000-290878, filed Sep. 25, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electric motor for a vehicle or an acoustic device.
2. Description of the Related Art
An ordinary electric motor for a vehicle such as a windshield wiper motor or a washer pump motor has a noise suppressing circuit that is comprised of a pair of noise suppressing coils and a capacitor. The noise suppressing circuit is effective to reduce electromagnetic noises generated at a commutator of the motor. However, if such the motor employs a pair of resinous bearing holders for supporting a pair of bearings that rotatably supports a shaft of a rotor, the resinous bearing holders electrically insulate the shaft from a ground. As a result, electro-magnetic noises may be radiated from an end of the shaft that extends from a case of the motor.
JP-U-6-9355 discloses an arrangement of grounding a shaft. In the arrangement, a metal bearing is in direct contact with a yoke that is grounded.
However, if the shaft is vibrated in the radial direction of the motor, the contact between the metal bearing and the yoke may be broken repeatedly, and the electro-magnetic noises cannot be effectively reduced.
A main object of the invention is to provide an electric motor that has an improved arrangement for reducing such electro-magnetic noises.
According to a main feature of the invention, a motor includes a conductive case, a member for grounding said case, a shaft and means for pressing a conducting member between the shaft and the case.
Therefore, the contact between the shaft and the case may not be broken even if the shaft is vibrated repeatedly.
The means may include a resilient contact member integrated with the case.
The means may include a conductive bearing holder fixed to the case and having a resilient contact member in contact with the bearing.
The means may include a magnetic core and a permanent magnet disposed to generate a magnetic force to press the contact member against the bearing.
The means may also include a spring washer held between the bearing and a collar formed on the shaft or a bearing-holding washer having a resilient projecting member.
The means may include a oil seal made of a conductive material.